Johny
Have a look at the plate on the side of the alternator. Will proberly be 55 amps.
You must realise that having 3 batteries hooked up without an isolating switch or device, is a no no. The alternator will deliver only to the battery with the least amount of internal resistance.
So if you have one buggered battery it will get all the charge and your good batteries nil.
Also if all your batteries are connected together ie no isolating switch then they will go down to the level of the least charged cell. In other words ,one bad battery will drag the other good one down to its level of discharge.
With an isolating switch to seperate the batteries your alternator should be able to handle 3 batteries.
Mine does.
Frank


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